// MIT License

// Copyright (c) 2018 Andy Pan

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package ants

import (
	"context"
	"sync"
	"sync/atomic"
	"time"

	syncx "github.com/panjf2000/ants/v2/internal/sync"
)

type poolCommon struct {
	// capacity of the pool, a negative value means that the capacity of pool is limitless, an infinite pool is used to
	// avoid potential issue of endless blocking caused by nested usage of a pool: submitting a task to pool
	// which submits a new task to the same pool.
	capacity int32

	// running is the number of the currently running goroutines.
	running int32

	// lock for protecting the worker queue.
	lock sync.Locker

	// workers is a slice that store the available workers.
	workers workerQueue

	// state is used to notice the pool to closed itself.
	state int32

	// cond for waiting to get an idle worker.
	cond *sync.Cond

	// done is used to indicate that all workers are done.
	allDone chan struct{}
	// once is used to make sure the pool is closed just once.
	once *sync.Once

	// workerCache speeds up the obtainment of a usable worker in function:retrieveWorker.
	workerCache sync.Pool

	// waiting is the number of goroutines already been blocked on pool.Submit(), protected by pool.lock
	waiting int32

	purgeDone int32
	purgeCtx  context.Context
	stopPurge context.CancelFunc

	ticktockDone int32
	ticktockCtx  context.Context
	stopTicktock context.CancelFunc

	now atomic.Value

	options *Options
}

// Pool accepts the tasks and process them concurrently,
// it limits the total of goroutines to a given number by recycling goroutines.
type Pool struct {
	poolCommon
}

// purgeStaleWorkers clears stale workers periodically, it runs in an individual goroutine, as a scavenger.
func (p *Pool) purgeStaleWorkers() {
	ticker := time.NewTicker(p.options.ExpiryDuration)

	defer func() {
		ticker.Stop()
		atomic.StoreInt32(&p.purgeDone, 1)
	}()

	purgeCtx := p.purgeCtx // copy to the local variable to avoid race from Reboot()
	for {
		select {
		case <-purgeCtx.Done():
			return
		case <-ticker.C:
		}

		if p.IsClosed() {
			break
		}

		var isDormant bool
		p.lock.Lock()
		staleWorkers := p.workers.refresh(p.options.ExpiryDuration)
		n := p.Running()
		isDormant = n == 0 || n == len(staleWorkers)
		p.lock.Unlock()

		// Notify obsolete workers to stop.
		// This notification must be outside the p.lock, since w.task
		// may be blocking and may consume a lot of time if many workers
		// are located on non-local CPUs.
		for i := range staleWorkers {
			staleWorkers[i].finish()
			staleWorkers[i] = nil
		}

		// There might be a situation where all workers have been cleaned up (no worker is running),
		// while some invokers still are stuck in p.cond.Wait(), then we need to awake those invokers.
		if isDormant && p.Waiting() > 0 {
			p.cond.Broadcast()
		}
	}
}

// ticktock is a goroutine that updates the current time in the pool regularly.
func (p *Pool) ticktock() {
	ticker := time.NewTicker(nowTimeUpdateInterval)
	defer func() {
		ticker.Stop()
		atomic.StoreInt32(&p.ticktockDone, 1)
	}()

	ticktockCtx := p.ticktockCtx // copy to the local variable to avoid race from Reboot()
	for {
		select {
		case <-ticktockCtx.Done():
			return
		case <-ticker.C:
		}

		if p.IsClosed() {
			break
		}

		p.now.Store(time.Now())
	}
}

func (p *Pool) goPurge() {
	if p.options.DisablePurge {
		return
	}

	// Start a goroutine to clean up expired workers periodically.
	p.purgeCtx, p.stopPurge = context.WithCancel(context.Background())
	go p.purgeStaleWorkers()
}

func (p *Pool) goTicktock() {
	p.now.Store(time.Now())
	p.ticktockCtx, p.stopTicktock = context.WithCancel(context.Background())
	go p.ticktock()
}

func (p *Pool) nowTime() time.Time {
	return p.now.Load().(time.Time)
}

// NewPool instantiates a Pool with customized options.
func NewPool(size int, options ...Option) (*Pool, error) {
	if size <= 0 {
		size = -1
	}

	opts := loadOptions(options...)

	if !opts.DisablePurge {
		if expiry := opts.ExpiryDuration; expiry < 0 {
			return nil, ErrInvalidPoolExpiry
		} else if expiry == 0 {
			opts.ExpiryDuration = DefaultCleanIntervalTime
		}
	}

	if opts.Logger == nil {
		opts.Logger = defaultLogger
	}

	p := &Pool{poolCommon: poolCommon{
		capacity: int32(size),
		allDone:  make(chan struct{}),
		lock:     syncx.NewSpinLock(),
		once:     &sync.Once{},
		options:  opts,
	}}
	p.workerCache.New = func() interface{} {
		return &goWorker{
			pool: p,
			task: make(chan func(), workerChanCap),
		}
	}
	if p.options.PreAlloc {
		if size == -1 {
			return nil, ErrInvalidPreAllocSize
		}
		p.workers = newWorkerQueue(queueTypeLoopQueue, size)
	} else {
		p.workers = newWorkerQueue(queueTypeStack, 0)
	}

	p.cond = sync.NewCond(p.lock)

	p.goPurge()
	p.goTicktock()

	return p, nil
}

// Submit submits a task to this pool.
//
// Note that you are allowed to call Pool.Submit() from the current Pool.Submit(),
// but what calls for special attention is that you will get blocked with the last
// Pool.Submit() call once the current Pool runs out of its capacity, and to avoid this,
// you should instantiate a Pool with ants.WithNonblocking(true).
func (p *Pool) Submit(task func()) error {
	if p.IsClosed() {
		return ErrPoolClosed
	}

	w, err := p.retrieveWorker()
	if w != nil {
		w.inputFunc(task)
	}
	return err
}

// Running returns the number of workers currently running.
func (p *Pool) Running() int {
	return int(atomic.LoadInt32(&p.running))
}

// Free returns the number of available workers, -1 indicates this pool is unlimited.
func (p *Pool) Free() int {
	c := p.Cap()
	if c < 0 {
		return -1
	}
	return c - p.Running()
}

// Waiting returns the number of tasks waiting to be executed.
func (p *Pool) Waiting() int {
	return int(atomic.LoadInt32(&p.waiting))
}

// Cap returns the capacity of this pool.
func (p *Pool) Cap() int {
	return int(atomic.LoadInt32(&p.capacity))
}

// Tune changes the capacity of this pool, note that it is noneffective to the infinite or pre-allocation pool.
func (p *Pool) Tune(size int) {
	capacity := p.Cap()
	if capacity == -1 || size <= 0 || size == capacity || p.options.PreAlloc {
		return
	}
	atomic.StoreInt32(&p.capacity, int32(size))
	if size > capacity {
		if size-capacity == 1 {
			p.cond.Signal()
			return
		}
		p.cond.Broadcast()
	}
}

// IsClosed indicates whether the pool is closed.
func (p *Pool) IsClosed() bool {
	return atomic.LoadInt32(&p.state) == CLOSED
}

// Release closes this pool and releases the worker queue.
func (p *Pool) Release() {
	if !atomic.CompareAndSwapInt32(&p.state, OPENED, CLOSED) {
		return
	}

	if p.stopPurge != nil {
		p.stopPurge()
		p.stopPurge = nil
	}
	if p.stopTicktock != nil {
		p.stopTicktock()
		p.stopTicktock = nil
	}

	p.lock.Lock()
	p.workers.reset()
	p.lock.Unlock()
	// There might be some callers waiting in retrieveWorker(), so we need to wake them up to prevent
	// those callers blocking infinitely.
	p.cond.Broadcast()
}

// ReleaseTimeout is like Release but with a timeout, it waits all workers to exit before timing out.
func (p *Pool) ReleaseTimeout(timeout time.Duration) error {
	if p.IsClosed() || (!p.options.DisablePurge && p.stopPurge == nil) || p.stopTicktock == nil {
		return ErrPoolClosed
	}

	p.Release()

	var purgeCh <-chan struct{}
	if !p.options.DisablePurge {
		purgeCh = p.purgeCtx.Done()
	} else {
		purgeCh = p.allDone
	}

	if p.Running() == 0 {
		p.once.Do(func() {
			close(p.allDone)
		})
	}

	timer := time.NewTimer(timeout)
	defer timer.Stop()
	for {
		select {
		case <-timer.C:
			return ErrTimeout
		case <-p.allDone:
			<-purgeCh
			<-p.ticktockCtx.Done()
			if p.Running() == 0 &&
				(p.options.DisablePurge || atomic.LoadInt32(&p.purgeDone) == 1) &&
				atomic.LoadInt32(&p.ticktockDone) == 1 {
				return nil
			}
		}
	}
}

// Reboot reboots a closed pool, it does nothing if the pool is not closed.
// If you intend to reboot a closed pool, use ReleaseTimeout() instead of
// Release() to ensure that all workers are stopped and resource are released
// before rebooting, otherwise you may run into data race.
func (p *Pool) Reboot() {
	if atomic.CompareAndSwapInt32(&p.state, CLOSED, OPENED) {
		atomic.StoreInt32(&p.purgeDone, 0)
		p.goPurge()
		atomic.StoreInt32(&p.ticktockDone, 0)
		p.goTicktock()
		p.allDone = make(chan struct{})
		p.once = &sync.Once{}
	}
}

func (p *Pool) addRunning(delta int) int {
	return int(atomic.AddInt32(&p.running, int32(delta)))
}

func (p *Pool) addWaiting(delta int) {
	atomic.AddInt32(&p.waiting, int32(delta))
}

// retrieveWorker returns an available worker to run the tasks.
func (p *Pool) retrieveWorker() (w worker, err error) {
	p.lock.Lock()

retry:
	// First try to fetch the worker from the queue.
	if w = p.workers.detach(); w != nil {
		p.lock.Unlock()
		return
	}

	// If the worker queue is empty, and we don't run out of the pool capacity,
	// then just spawn a new worker goroutine.
	if capacity := p.Cap(); capacity == -1 || capacity > p.Running() {
		p.lock.Unlock()
		w = p.workerCache.Get().(*goWorker)
		w.run()
		return
	}

	// Bail out early if it's in nonblocking mode or the number of pending callers reaches the maximum limit value.
	if p.options.Nonblocking || (p.options.MaxBlockingTasks != 0 && p.Waiting() >= p.options.MaxBlockingTasks) {
		p.lock.Unlock()
		return nil, ErrPoolOverload
	}

	// Otherwise, we'll have to keep them blocked and wait for at least one worker to be put back into pool.
	p.addWaiting(1)
	p.cond.Wait() // block and wait for an available worker
	p.addWaiting(-1)

	if p.IsClosed() {
		p.lock.Unlock()
		return nil, ErrPoolClosed
	}

	goto retry
}

// revertWorker puts a worker back into free pool, recycling the goroutines.
func (p *Pool) revertWorker(worker *goWorker) bool {
	if capacity := p.Cap(); (capacity > 0 && p.Running() > capacity) || p.IsClosed() {
		p.cond.Broadcast()
		return false
	}

	worker.lastUsed = p.nowTime()

	p.lock.Lock()
	// To avoid memory leaks, add a double check in the lock scope.
	// Issue: https://github.com/panjf2000/ants/issues/113
	if p.IsClosed() {
		p.lock.Unlock()
		return false
	}
	if err := p.workers.insert(worker); err != nil {
		p.lock.Unlock()
		return false
	}
	// Notify the invoker stuck in 'retrieveWorker()' of there is an available worker in the worker queue.
	p.cond.Signal()
	p.lock.Unlock()

	return true
}
